Once an opinion is published, that case can be used to interpret other cases and can itself be subject to further interpretation by these cases.  Once a particular case has been identified in the course of research, it should be analyzed through Shepard's to see how it has stood against possible subsequent interpretation in later cases. These later cases can then examined to see if they will be useful or harmful.   This process is called Shepardizing.  Shepard's is available through Nexis Uni (Lexis Nexis).  Shepard's can only be searched by a case's citation so you must have that information before using it.  The images below demonstrate how to interpret the results of the search of Metromedia v. City of San Diego, which is cited as 453 U.S. 490. 

All of the citing decisions are also linked to the full text of the whole opinion as well as the individual page.